<?php  // $Id: lexer.php,v 1.1 2005/01/31 07:39:03 moodler Exp $

/* PHP lexer code snarfed from the CVS tree for the lamplib project at 
 * http://sourceforge.net/projects/lamplib
 * This project is administered by Markus Baker, Harry Fuecks and Matt
 * Mitchell, and the project  code is in the public domain.
 * 
 * Thanks, guys!
 */

	define("LEXER_ENTER", 1);
	define("LEXER_MATCHED", 2);
	define("LEXER_UNMATCHED", 3);
	define("LEXER_EXIT", 4);
	define("LEXER_SPECIAL", 5);
	
	/**
	 *	Compounded regular expression. Any of
	 *	the contained patterns could match and
	 *	when one does it's label is returned.
	 */
	class ParallelRegex {
		var $_patterns;
		var $_labels;
		var $_regex;
		var $_case;
		
		/**
		 *	Constructor. Starts with no patterns.
		 *	@param $case	True for case sensitive, false
		 *					for insensitive.
		 *	@public
		 */
		function ParallelRegex($case) {
			$this->_case = $case;
			$this->_patterns = array();
			$this->_labels = array();
			$this->_regex = null;
		}
		
		/**
		 *	Adds a pattern with an optional label.
		 *	@param $pattern	  Perl style regex, but ( and )
		 *						 lose the usual meaning.
		 *	@param $label		Label of regex to be returned
		 *						 on a match.
		 *	@public
		 */
		function addPattern($pattern, $label = true) {
			$count = count($this->_patterns);
			$this->_patterns[$count] = $pattern;
			$this->_labels[$count] = $label;
			$this->_regex = null;
		}
		
		/**
		 *	Attempts to match all patterns at once against
		 *	a string.
		 *	@param $subject	  String to match against.
		 *	@param $match		First matched portion of
		 *						 subject.
		 *	@return			  True on success.
		 *	@public
		 */
		function match($subject, &$match) {
			if (count($this->_patterns) == 0) {
				return false;
			}
			if (!preg_match($this->_getCompoundedRegex(), $subject, $matches)) {
				$match = "";
				return false;
			}
			$match = $matches[0];
			for ($i = 1; $i < count($matches); $i++) {
				if ($matches[$i]) {
					return $this->_labels[$i - 1];
				}
			}
			return true;
		}
		
		/**
		 *	Compounds the patterns into a single
		 *	regular expression separated with the
		 *	"or" operator. Caches the regex.
		 *	Will automatically escape (, ) and / tokens.
		 *	@param $patterns	List of patterns in order.
		 *	@private
		 */
		function _getCompoundedRegex() {
			if ($this->_regex == null) {
				for ($i = 0; $i < count($this->_patterns); $i++) {
					$this->_patterns[$i] = '(' . str_replace(
							array('/', '(', ')'),
							array('\/', '\(', '\)'),
							$this->_patterns[$i]) . ')';
				}
				$this->_regex = "/" . implode("|", $this->_patterns) . "/" . $this->_getPerlMatchingFlags();
			}
			return $this->_regex;
		}
		
		/**
		 *	Accessor for perl regex mode flags to use.
		 *	@return		Flags as string.
		 *	@private
		 */
		function _getPerlMatchingFlags() {
			return ($this->_case ? "msS" : "msSi");
		}
	}
	
	/**
	 *	States for a stack machine.
	 */
	class StateStack {
		var $_stack;
		
		/**
		 *	Constructor. Starts in named state.
		 *	@param $start		Starting state name.
		 *	@public
		 */
		function StateStack($start) {
			$this->_stack = array($start);
		}
		
		/**
		 *	Accessor for current state.
		 *	@return		State as string.
		 *	@public
		 */
		function getCurrent() {
			return $this->_stack[count($this->_stack) - 1];
		}
		
		/**
		 *	Adds a state to the stack and sets it
		 *	to be the current state.
		 *	@param $state		New state.
		 *	@public
		 */
		function enter($state) {
			array_push($this->_stack, $state);
		}
		
		/**
		 *	Leaves the current state and reverts
		 *	to the previous one.
		 *	@return	 False if we drop off
		 *				the bottom of the list.
		 *	@public
		 */
		function leave() {
			if (count($this->_stack) == 1) {
				return false;
			}
			array_pop($this->_stack);
			return true;
		}
	}
	
	/**
	 *	Accepts text and breaks it into tokens.
	 *	Some optimisation to make the sure the
	 *	content is only scanned by the PHP regex
	 *	parser once. Lexer modes must not start
	 *	with leading underscores.
	 */
	class Lexer {
		var $_regexes;
		var $_parser;
		var $_mode;
		var $_mode_handlers;
		var $_case;
		
		/**
		 *	Sets up the lexer in case insensitive matching
		 *	by default.
		 *	@param $parser	 Handling strategy by
		 *					   reference.
		 *	@param $start	  Starting handler.
		 *	@param $case	   True for case sensitive.
		 *	@public
		 */
		function Lexer(&$parser, $start = "accept", $case = false) {
			$this->_case = $case;
			$this->_regexes = array();
			$this->_parser = &$parser;
			$this->_mode = new StateStack($start);
			$this->_mode_handlers = array();
		}
		
		/**
		 *	Adds a token search pattern for a particular
		 *	parsing mode. The pattern does not change the
		 *	current mode.
		 *	@param $pattern	  Perl style regex, but ( and )
		 *						 lose the usual meaning.
		 *	@param $mode		 Should only apply this
		 *						 pattern when dealing with
		 *						 this type of input.
		 *	@public
		 */
		function addPattern($pattern, $mode = "accept") {
			if (!isset($this->_regexes[$mode])) {
				$this->_regexes[$mode] = new ParallelRegex($this->_case);
			}
			$this->_regexes[$mode]->addPattern($pattern);
		}
		
		/**
		 *	Adds a pattern that will enter a new parsing
		 *	mode. Useful for entering parenthesis, strings,
		 *	tags, etc.
		 *	@param $pattern	  Perl style regex, but ( and )
		 *						 lose the usual meaning.
		 *	@param $mode		 Should only apply this
		 *						 pattern when dealing with
		 *						 this type of input.
		 *	@param $new_mode	 Change parsing to this new
		 *						 nested mode.
		 *	@public
		 */
		function addEntryPattern($pattern, $mode, $new_mode) {
			if (!isset($this->_regexes[$mode])) {
				$this->_regexes[$mode] = new ParallelRegex($this->_case);
			}
			$this->_regexes[$mode]->addPattern($pattern, $new_mode);
		}
		
		/**
		 *	Adds a pattern that will exit the current mode
		 *	and re-enter the previous one.
		 *	@param $pattern	  Perl style regex, but ( and )
		 *						 lose the usual meaning.
		 *	@param $mode		 Mode to leave.
		 *	@public
		 */
		function addExitPattern($pattern, $mode) {
			if (!isset($this->_regexes[$mode])) {
				$this->_regexes[$mode] = new ParallelRegex($this->_case);
			}
			$this->_regexes[$mode]->addPattern($pattern, "__exit");
		}
		
		/**
		 *	Adds a pattern that has a special mode.
		 *	Acts as an entry and exit pattern in one go.
		 *	@param $pattern	  Perl style regex, but ( and )
		 *						 lose the usual meaning.
		 *	@param $mode		 Should only apply this
		 *						 pattern when dealing with
		 *						 this type of input.
		 *	@param $special	  Use this mode for this one token.
		 *	@public
		 */
		function addSpecialPattern($pattern, $mode, $special) {
			if (!isset($this->_regexes[$mode])) {
				$this->_regexes[$mode] = new ParallelRegex($this->_case);
			}
			$this->_regexes[$mode]->addPattern($pattern, "_$special");
		}
		
		/**
		 *	Adds a mapping from a mode to another handler.
		 *	@param $mode		Mode to be remapped.
		 *	@param $handler	 New target handler.
		 *	@public
		 */
		function mapHandler($mode, $handler) {
			$this->_mode_handlers[$mode] = $handler;
		}
		
		/**
		 *	Splits the page text into tokens. Will fail
		 *	if the handlers report an error or if no
		 *	content is consumed. If successful then each
		 *	unparsed and parsed token invokes a call to the
		 *	held listener.
		 *	@param $raw		Raw HTML text.
		 *	@return			True on success, else false.
		 *	@public
		 */
		function parse($raw) {
			if (!isset($this->_parser)) {
				return false;
			}
			$length = strlen($raw);
			while (is_array($parsed = $this->_reduce($raw))) {
				list($unmatched, $matched, $mode) = $parsed;
				if (!$this->_dispatchTokens($unmatched, $matched, $mode)) {
					return false;
				}
				if (strlen($raw) == $length) {
					return false;
				}
				$length = strlen($raw);
			}
			if (!$parsed) {
				return false;
			}
			return $this->_invokeParser($raw, LEXER_UNMATCHED);
		}
		
		/**
		 *	Sends the matched token and any leading unmatched
		 *	text to the parser changing the lexer to a new
		 *	mode if one is listed.
		 *	@param $unmatched	Unmatched leading portion.
		 *	@param $matched	  Actual token match.
		 *	@param $mode		 Mode after match. The "_exit"
		 *						 mode causes a stack pop. An
		 *						 false mode causes no change.
		 *	@return			  False if there was any error
		 *						 from the parser.
		 *	@private
		 */
		function _dispatchTokens($unmatched, $matched, $mode = false) {
			if (!$this->_invokeParser($unmatched, LEXER_UNMATCHED)) {
				return false;
			}
			if ($mode === "__exit") {
				if (!$this->_invokeParser($matched, LEXER_EXIT)) {
					return false;
				}
				return $this->_mode->leave();
			}
			if (strncmp($mode, "_", 1) == 0) {
				$mode = substr($mode, 1);
				$this->_mode->enter($mode);
				if (!$this->_invokeParser($matched, LEXER_SPECIAL)) {
					return false;
				}
				return $this->_mode->leave();
			}
			if (is_string($mode)) {
				$this->_mode->enter($mode);
				return $this->_invokeParser($matched, LEXER_ENTER);
			}
			return $this->_invokeParser($matched, LEXER_MATCHED);
		}
		
		/**
		 *	Calls the parser method named after the current
		 *	mode. Empty content will be ignored.
		 *	@param $content		Text parsed.
		 *	@param $is_match	   Token is recognised rather
		 *						   than unparsed data.
		 *	@private
		 */
		function _invokeParser($content, $is_match) {
			if (($content === "") || ($content === false)) {
				return true;
			}
			$handler = $this->_mode->getCurrent();
			if (isset($this->_mode_handlers[$handler])) {
				$handler = $this->_mode_handlers[$handler];
			}
			return $this->_parser->$handler($content, $is_match);
		}
		
		/**
		 *	Tries to match a chunk of text and if successful
		 *	removes the recognised chunk and any leading
		 *	unparsed data. Empty strings will not be matched.
		 *	@param $raw		 The subject to parse. This is the
		 *						content that will be eaten.
		 *	@return			 Three item list of unparsed
		 *						content followed by the
		 *						recognised token and finally the
		 *						action the parser is to take.
		 *						True if no match, false if there
		 *						is a parsing error.
		 *	@private
		 */
		function _reduce(&$raw) {
			if (!isset($this->_regexes[$this->_mode->getCurrent()])) {
				return false;
			}
			if ($raw === "") {
				return true;
			}
			if ($action = $this->_regexes[$this->_mode->getCurrent()]->match($raw, $match)) {
				$count = strpos($raw, $match);
				$unparsed = substr($raw, 0, $count);
				$raw = substr($raw, $count + strlen($match));
				return array($unparsed, $match, $action);
			}
			return true;
		}
	}
?>
